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Geography > Rivers > Flashcards

Rivers Flashcards

1
Q

Drainage Basin

A

An area of land drained by a river and its tributaries

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2
Q

Source

A

The start of a river

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3
Q

Tributary

A

A stream or river that flows into a larger river

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4
Q

Confluence

A

Where a tributary joins the river

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5
Q

Long profile shape

A

Upper course - Steep gradient

Middle course - Gentle gradient

Lower course - Very gentle gradient

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6
Q

Cross profile shape

A

Upper Course - Steep V-Shaped valley, narrow and shallow turbulent river

Middle Course - Valley with wider, flatter bed. Wider and deeper river

Lower Course - Very wide and flat valley. Wide, deep river with large sediment load

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7
Q

Why does the cross profile change over the course of the river?

A
  • More water joins from more tributaries
  • So more energy to erode larger channel
  • Through processes such as abrasion, hydraulic action, etc
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8
Q

Why does velocity increase downstream?

A
  • Upper course is shallower, so more energy is lost through friction between water and banks
  • In the lower courses, water depth is greater so less water is in contact with the banks so river flows faster DESPITE SHALLOWR GRADIENT
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9
Q

Hydraulic Action

A

Where the force of water breaks rock particles away from the river channel

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10
Q

Abrasion

A

The eroding away of the river channel by rocks carried with the flow of the river

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11
Q

Attrition

A
  • Stones carried by river hit each other

- Breaking down and rounding eachother

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12
Q

Solution / Corrosion

A

Mildly acidic river water dissolves limestone and chalk

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13
Q

Traction

A

Large boulders and rocks are rolled along river bed

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14
Q

Saltation

A

Small pebbles and stones bounce along river bed

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15
Q

Suspension

A
  • Small particles are carried along by the water

- Such as silt or clay

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16
Q

Solution

A

Dissolved load

17
Q

Typical Landforms in each course

A

Upper course - Interlocking spurs, V-shaped valley, gorges, waterfalls

Middle course - Meanders, OX-bow lakes

Lower course - Levees, flood plains, river estuaries

18
Q

Interlocking spurs formation

A
  1. V-Shaped valley created by erosion vertically downwards
  2. Rivers aren’t powerful enough to erode laterally
  3. So wind around the high hillsides in the way
  4. Hillsides interlock as river winds round them
  5. Interlocking spurs is formed
19
Q

Waterfall formation

A
  1. River flows over hard rock lying on top of soft rock
  2. River erodes soft rock faster, developing a vertical drop where hard rock and soft rock meets
  3. Plunge pool forms from force of falling water (hydraulic action)
  4. Rock above plunge pool is undercut and left hanging
  5. Overhanging hard rock eventually collapses due to force of gravity
  6. Erosion continues to undercut underneath the hard rock
  7. So the process repeats and the waterfall over time retreats upstream
20
Q

Gorge formations

A
  • Waterfall retreats upstream
  • Leaving narrow, steep sided valleys called GORGES
  • Also form at the end of glacial periods from meltwater
21
Q

Meander

A
  • Wide bend in the river found mainly in lowland areas

- Most efficient course of river in gentle slopes

22
Q

Meander formation

A
  • water levels travel faster on the outside of the bend
  • so more lateral erosion takes place
  • widening meanders
  • deposition also occurs mainly in the insides of the bend
23
Q

What are pools

A

Deep water found on the outside of bends (faster flow, more vertical Erosion)

24
Q

What are riffles

A

Riffles are shallow pools of water formed by the deposition of coarse sediment

25
Q

Ox-bow lake formation

A
  1. Meander is created
  2. Erosion through hydraulic action bends river so that the meanders travel towards each other
  3. The neck of the meander eventually breaks creating a straight river
  4. The old meander becomes blocked from the main river by deposition, creating a separate ox-bow lake
26
Q

Deposition

A
  • Deposition is the dropping of the river’s load
  • when the water velocity decreases so does not have enough energy to transport the sediment
  • occurs mainly in the lower course of the river
27
Q

Floodplain

A

Wide flat area of marshy land on either side of the river

  • occurs mainly in middle and lower courses
28
Q

Levee

A

An enlarged bank built up on each side of the river by deposition during river flooding

29
Q

Estuary

A

The tidal mouth of a large river, where tide meets the stream

  • a transitional zone between fluvial and coastal processes
30
Q

Physical factors affecting flood risk

A

Precipitation - high amounts of rain can cause rivers to flood

Geology - impermeable rocks force water to flow, decreasing lag time and increasing flood risk because ground cannot absorb water

Relief - steeper mountain environments cause rapid flow of water

31
Q

Lag time

A

The time between the peak rainfall and peak discharge

32
Q

Human factors affecting flood risk

A

Urbanisation- impermeable surfaces such as roads aid water flow and decrease lag time

Deforestation - less interception of water, lag time increases and aids water flow

Agriculture - increased surface runoff from unused soil

33
Q

What are hydrographs

A

Graph plotting river discharge measured in cumecs, against against time after a storm

34
Q

Hard engineering strategies

A
  • dams / reservoirs regulate water flow (eg. Clywedog reservoir)
  • by-pass channels to cut through meanders to reduce flood risk through urbanised areas
  • channel straightening lined with concrete for faster flow of water through urbanised areas
  • channel enlarged by dredging
35
Q

Costs / benefits of channel straightening

A
  • can reduce risk for vulnerable areas
  • however shifts problem downstream
  • creates an unnatural environment, destroying riverside habitats
36
Q

Flood relief channels

A
  • Building new artificial channels which are used when a river is close to maximum discharge
  • take pressure off main channels when floods are likely
  • thus reducing flood risk
  • eg. Jubilee Rivee
37
Q

Soft engineering strategies

A
  • afforestation to increase interception of water
  • Wetland areas used for water storage
  • river bank conservation, eg. Planting trees
  • flood warning / preparation

Geography (26 decks)

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